Low-Shear Stress Promotes Atherosclerosis via Inducing Endothelial Cell Pyroptosis Mediated by IKKε/STAT1/NLRP3 Pathway

Atherosclerosis is initiated by vascular endothelial dysfunction, and low-shear stress (LSS) of blood flow is a key factor leading to endothelial dysfunction. Growing evidence suggests that endothelial cell pyroptosis plays an important role in the development of atherosclerosis. Studies have shown that low-shear stress can induce endothelial cell pyroptosis, but the exact mechanism remains unclear. Our experiments demonstrated that low-shear stress induced endothelial cell pyroptosis and the phosphorylation of IκB kinase ε (IKKε). IKKε knockdown not only significantly attenuated atherosclerosis lesions of aortic arch areas in ApoE-/- mice fed with high cholesterol diets, but also markedly reduced endothelial cell pyroptosis and NLRP3 expression triggered by low-shear stress. Further mechanism studies showed that IKKε promoted the expression of NLRP3 via activating signal transducer and activator of transcription 1 (STAT1) and the subsequent binding of STAT1 to NLRP3 promoter region. These results suggest that low-shear stress plays a pro-atherosclerotic role by promoting endothelial cell pyroptosis through the IKKε/STAT1/NLRP3 pathway, which provides new insights into the formation of atherosclerosis.

Molecular cloning and functional characterization of pigeon IKKε

Inhibitor of nuclear factor kappa-B kinase ε (IKKε), a member of the non-canonical IκB kinase family, plays a critical role in connecting various signaling pathways associated with the initiation of type I interferon (IFN) production. Although the importance of IKKε in innate immunity has been well established in mammals and fish, its characterization and function in pigeons have remained largely unexplored. In this study, we successfully cloned pigeon IKKε (piIKKε) from pigeon embryo fibroblasts (PEFs) for the first time. This gene encodes 722 amino acids and shares high amino acid similarity with its duck and goose counterparts. piIKKε showed a diffuse cytoplasmic distribution and broad expression in all tissues examined. Overexpression of piIKKε in PEFs significantly activated the IFN-β promoter, with both the kinase and CC domains of piIKKε playing key roles in initiating IFN-β expression. Knockdown of piIKKε using small interfering RNA significantly reduced the levels of IFN-β induced by NDV, AIV, poly (I:C), or SeV. Furthermore, the presence of piIKKε resulted in a remarkable reduction in the replication of both avian influenza virus (AIV) H9N2 and Newcastle disease virus (NDV) in PEFs. Our results demonstrate that piIKKε plays a critical role in mediating antiviral innate immunity in pigeons.

DLG1 promotes the antiviral innate immune response by inhibiting p62-mediated autophagic degradation of IKKε

IMPORTANCE

The type-I interferon (IFN-I) signaling pathway is the first line of antiviral innate immunity. It must be precisely regulated against virus-induced damage. The tightly regulated mechanisms of action of host genes in the antiviral innate immune signaling pathway are still worth studying. Here, we report a novel role of DLG1 in positively regulating the IκB kinase epsilon (IKKε)-mediated IFN-I signaling response against negative-stranded RNA virus replication, whereas the RNA virus inhibits the expression of DLG1 for immune escape. Importantly, the E3 ligase March2 interacts with and promotes K27-linked polyubiquitination of IKKε, and p62 is a cargo receptor that recognizes ubiquitinated IKKε for eventual autophagic degradation. Together, the current findings elucidate the role of DLG1 in the antiviral IFN-I signaling pathway and viral infection repression.

TRIM25 negatively regulates IKKε-mediated interferon signaling in black carp

IKKε plays an important role in the activation of IRF3/IRF7 and the production of interferon (IFN), however, its regulation remains obscure in human. E3 ligase TRIM25 has been reported to manipulate the K63-linked ubiquitination of RIG-I, leading to the activation of RIG-I/IFN signaling. To elucidate the role of TRIM25 in teleost, a TRIM25 homolog (bcTRIM25) was cloned and characterized from black carp (Mylopharyngodon piceus). bcTRIM25 contains 653 amino acids, possessing conservative RING, B-box and SPRY domain, which is highly expressed in muscle, spleen and skin. bcTRIM25 knock-down enhanced the antiviral ability of host cells. bcTRIM25 over-expression alone in EPC cells attenuated bcIFNa promoter transcription in the reporter assays and impeded PKR and MX1 expression in qRT-PCR. Interestingly, co-IP assays indicated that bcTRIM25 interacted with bcIKKε and the induced bcIFNa promoter transcription by bcIKKε was notably hindered by bcTRIM25. Furthermore, bcIKKε-induced expression of interferon stimulated genes (ISGs) and antiviral activity were dampened by bcTRIM25. Further exploration showed that bcTRIM25 visibly enhanced the ubiquitination of bcIKKε but significantly attenuated the phosphorylation of bcIKKε. Thus, our data demonstrate for the first time in vertebrate that TRIM25 negatively regulates IKKε through enhancing its ubiquitination, which sheds a light on the regulation of IKKε/IFN signaling.

Porcine IKKε is involved in the STING-induced type I IFN antiviral response of the cytosolic DNA signaling pathway

The cyclic GMP-AMP synthase and stimulator of interferon (IFN) genes (cGAS-STING) pathway serves as a crucial component of innate immune defense and exerts immense antiviral activity by inducing the expression of type I IFNs. Currently, STING-activated production of type I IFNs has been thought to be mediated only by TANK-binding kinase 1 (TBK1). Here, we identified that porcine IKKε (pIKKε) is also directly involved in STING-induced type I IFN expression and antiviral response by using IKKε-/- porcine macrophages. Similar to pTBK1, pIKKε interacts directly with pSTING on the C-terminal tail. Furthermore, the TBK1-binding motif of pSTING C-terminal tail is essential for its interaction with pIKKε, and within the TBK1-binding motif, the leucine (L) 373 is also critical for the interaction. On the other hand, both kinase domain and scaffold dimerization domain of pIKKε participate in the interactions with pSTING. Consistently, the reconstitution of pIKKε and its mutants in IKKε-/- porcine macrophages corroborated that IKKε and its kinase domain and scaffold dimerization domain are all involved in the STING signaling and antiviral function. Thus, our findings deepen the understanding of porcine cGAS-STING pathway, which lays a foundation for effective antiviral therapeutics against porcine viral diseases.

SAMHD1 impairs type I interferon induction through the MAVS, IKKε, and IRF7 signaling axis during viral infection

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) restricts human immunodeficiency virus type 1 (HIV-1) infection by reducing the intracellular dNTP pool. We have shown that SAMHD1 suppresses nuclear factor kappa-B activation and type I interferon (IFN-I) induction by viral infection and inflammatory stimuli. However, the mechanism by which SAMHD1 inhibits IFN-I remains unclear. Here, we show that SAMHD1 inhibits IFN-I activation induced by the mitochondrial antiviral-signaling protein (MAVS). SAMHD1 interacted with MAVS and suppressed MAVS aggregation in response to Sendai virus infection in human monocytic THP-1 cells. This resulted in increased phosphorylation of TANK binding kinase 1 (TBK1), inhibitor of nuclear factor kappa-B kinase epsilon (IKKε), and IFN regulatory factor 3 (IRF3). SAMHD1 suppressed IFN-I activation induced by IKKε and prevented IRF7 binding to the kinase domain of IKKε. We found that SAMHD1 interaction with the inhibitory domain (ID) of IRF7 (IRF7-ID) was necessary and sufficient for SAMHD1 suppression of IRF7-mediated IFN-I activation in HEK293T cells. Computational docking and molecular dynamics simulations revealed possible binding sites between IRF7-ID and full-length SAMHD1. Individual substitution of F411, E416, or V460 in IRF7-ID significantly reduced IRF7 transactivation activity and SAMHD1 binding. Furthermore, we investigated the role of SAMHD1 inhibition of IRF7-mediated IFN-I induction during HIV-1 infection. We found that THP-1 cells lacking IRF7 expression had reduced HIV-1 infection and viral transcription compared to control cells, indicating a positive role of IRF7 in HIV-1 infection. Our findings suggest that SAMHD1 suppresses IFN-I induction through the MAVS, IKKε, and IRF7 signaling axis.

Dengue Virus 2 NS2B Targets MAVS and IKKε to Evade the Antiviral Innate Immune Response

Dengue virus (DENV) is a widespread arbovirus. To efficiently establish infection, DENV evolves multiple strategies to hijack the host innate immune response. Herein, we examined the inhibitory effects of DENV serotype 2 (DENV2) nonstructural proteins on RIG-I-directed antiviral immune response. We found that DENV2 NS2A, NS2B, NS4A, and NS4B significantly inhibited RIG-I-mediated IFN-β promoter activation. The roles of NS2B in RIG-I-directed antiviral immune response are unknown. Our study further showed that NS2B could dose-dependently suppress RIG-I/MAVSinduced activation of IFN-β promoter. Consistently, NS2B significantly decreased RIG-I- and MAVSinduced transcription of IFNB1, ISG15, and ISG56. Mechanistically, NS2B was found to interact with MAVS and IKKε to impair RIG-I-directed antiviral response. Our findings demonstrated a previously uncharacterized function of NS2B in RIG-I-mediated antiviral response, making it a promising drug target for anti-DENV treatments.

Hepatitis C Virus Nonstructural Protein 5A Interacts with Immunomodulatory Kinase IKKε to Negatively Regulate Innate Antiviral Immunity

Hepatitis C virus (HCV) infection can lead to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. HCV employs diverse strategies to evade host antiviral innate immune responses to mediate a persistent infection. In the present study, we show that nonstructural protein 5A (NS5A) interacts with an NF-κB inhibitor immunomodulatory kinase, IKKε, and subsequently downregulats beta interferon (IFN-β) promoter activity. We further demonstrate that NS5A inhibits DDX3-mediated IKKε and interferon regulatory factor 3 (IRF3) phosphorylation. We also note that hyperphosphorylation of NS5A mediats protein interplay between NS5A and IKKε, thereby contributing to NS5A-mediated modulation of IFN-β signaling. Lastly, NS5A inhibits IKKε-dependent p65 phosphorylation and NF-κB activation. Based on these findings, we propose NS5A as a novel regulator of IFN signaling events, specifically by inhibiting IKKε downstream signaling cascades through its interaction with IKKε. Taken together, these data suggest an additional mechanistic means by which HCV modulates host antiviral innate immune responses to promote persistent viral infection.

The African swine fever virus protease pS273R inhibits DNA sensing cGAS-STING pathway by targeting IKKε

African swine fever virus (ASFV), a large and complex cytoplasmic double-stranded DNA virus, has developed multiple strategies to evade the antiviral innate immune responses. Cytosolic DNA arising from invading ASFV is mainly detected by the cyclic GMP-AMP synthase (cGAS) and then triggers a series of innate immune responses to prevent virus invasion. However, the immune escape mechanism of ASFV remains to be fully clarified. The pS273R of ASFV is a member of the SUMO-1-specific protease family and is crucial for valid virus replication. In this study, we identified pS273R as a suppressor of cGAS-STING pathway mediated type I interferon (IFN) production by ASFV genomic open reading frame screening. The pS273R was further confirmed as an inhibitor of IFN production as well as its downstream antiviral genes in cGAS-STING pathway. Mechanistically, pS273R greatly decreased the cGAS-STING signaling by targeting IKKε but not TBK1, and pS273R was found to disturb the interaction between IKKε and STING through its interaction with IKKε. Further, mutational analyses revealed that pS273R antagonized the cGAS-STING pathway by enzyme catalytic activity, which might affect the IKKε sumoylation state required for the interaction with STING. In summary, our results revealed for the first time that pS273R acts as an obvious negative regulator of cGAS-STING pathway by targeting IKKε via its enzymatic activity, which shows a new immune evasion mechanism of ASFV.

Regulation of IRF3 activation in Human Antiviral Signalling Pathways

The interferon regulatory factor (IRF) family of transcription factors play a vital role in the human innate antiviral immune responses with production of interferons (IFNs) as a hallmark outcome of activation. In recent years, IRF3 has been considered a principal early regulator of type I IFNs (TI-IFNs) directly downstream of intracellular virus sensing. Despite decades of research on IRF-activating pathways, many questions remain on the regulation of IRF3 activation. The kinases IκB kinase epsilon (IKKε) and TANK-binding kinase-1 (TBK1) and the scaffold proteins TRAF family member-associated NF-kappa-B activator (TANK), NF-kappa-B-activating kinase-associated protein 1 (NAP1) and TANK-binding kinase 1-binding protein 1 (TBKBP1)/similar to NAP1 TBK1 adaptor (SINTBAD) are believed to be core components of an IRF3-activation complex yet their contextual involvement and complex composition are still unclear. This review will give an overview of antiviral signaling pathways leading to the activation of IRF3 and discuss recent developments in our understanding of its proximal regulation.

DDX3X functionally and physically interacts with Estrogen Receptor-alpha

DEAD-box protein 3X (DDX3X) is a human DEAD-box protein with conventional roles in RNA metabolism and unconventional functions in signalling pathways that do not require its enzymatic activity. For example, DDX3X acts as a multifunctional adaptor molecule in anti-viral innate immune signalling pathways, where it interacts with and regulates the kinase IKB-kinase-epsilon (IIKKε). Interestingly, both DDX3X and IKKɛ have also independently been shown to act as breast cancer oncogenes. IKKɛ's oncogenic functions are likely multifactorial, but it was suggested to phosphorylate the transcription factor Estrogen receptor alpha (ERα) at Serine 167, which drives expression of Erα target genes in an estrogen-independent manner. In this study, we identified a novel physical interaction between DDX3X and ERα that positively regulates ERα activation. DDX3X knockdown in ER+ breast cancer cell lines resulted in reduced ERα phosphorylation, reduced Estrogen Response Element (ERE)-controlled reporter gene expression, decreased expression of ERα target genes, and decreased cell proliferation. Vice versa, overexpression of DDX3X resulted in enhanced ERα phosphorylation and activity. Furthermore, we provide evidence that DDX3X physically binds to ERα from co-immunoprecipitation and pulldown experiments. Based on our data, we propose that DDX3X acts as an adaptor to facilitate IKKε-mediated ERα activation, akin to the mechanism we previously elucidated for IKKε-mediated Interferon Regulatory factor 3 (IRF3) activation in innate immune signalling. In conclusion, our research provides a novel molecular mechanism that might contribute to the oncogenic effect of DDX3X in breast cancer, potentially linking it to the development of resistance against endocrine therapy.

TmIKKε Is Required to Confer Protection Against Gram-Negative Bacteria, E. coli by the Regulation of Antimicrobial Peptide Production in the Tenebrio molitor Fat Body

The inhibitor of nuclear factor-kappa B (NF-κB) kinase (IKK) is the core regulator of the NF-κB pathway against pathogenic invasion in vertebrates or invertebrates. IKKβ, -ε and -γ have pivotal roles in the Toll and immune deficiency (IMD) pathways. In this study, a homolog of IKKε (TmIKKε) was identified from Tenebrio molitor RNA sequence database and functionally characterized for its role in regulating immune signaling pathways in insects. The TmIKKε gene is characterized by two exons and one intron comprising an open reading frame (ORF) of 2,196 bp that putatively encodes a polypeptide of 731 amino acid residues. TmIKKε contains a serine/threonine protein kinases catalytic domain. Phylogenetic analysis established the close homology of TmIKKε to Tribolium castaneum IKKε (TcIKKε) and its proximity with other IKK-related kinases. The expression of TmIKKε mRNA was elevated in the gut, integument, and hemocytes of the last-instar larva and the fat body, Malpighian tubules, and testis of 5-day-old adults. TmIKKε expression was significantly induced by Escherichia coli, Staphylococcus aureus, and Candida albicans challenge in whole larvae and tissues, such as hemocytes, gut, and fat body. The knockdown of the TmIKKε messenger RNA (mRNA) expression significantly reduced the survival of the larvae against microbial challenges. Further, we investigated the induction patterns of 14 T. molitor antimicrobial peptides (AMPs) genes in TmIKKε gene-silencing model after microbial challenges. While in hemocytes, the transcriptional regulation of most AMPs was negatively regulated in the gut and fat body tissue of T. molitor, AMPs, such as TmTenecin 1, TmTenecin 4, TmDefensin, TmColeoptericin A, TmColeoptericin B, TmAttacin 1a, and TmAttacin 2, were positively regulated in TmIKKε-silenced individuals after microbial challenge. Collectively, the results implicate TmIKKε as an important factor in antimicrobial innate immune responses in T. molitor.

IKKε protects against starvation-induced NLRP3 inflammasome and pyroptosis in H9c2 cells by alleviating mitochondrial injury

The deprivation of myocardial nutrition causes cardiomyocyte death and disturbance of energy metabolism. IKKε plays an important regulatory role in many biological events such as inflammation, redox reaction, cell death, etc. However, the more in-depth mechanism by which IKKε contributes to cardiomyocytes death in nutrition deprivation remains poorly understood. IKKε expression was knocked down by siRNA in H9c2 cells, and cells were cultured under starvation conditions to simulate ischemic conditions. Starvation triggered greater NLRP3 activation, accompanied by more IL-1β, IL-18 and caspase-1 release in the siIKKε H9c2 cells compared with the control H9c2 cells. Western blot and immunofluorescence showed that the IKKε konckdown promoted NLRP3 expressions and ROS release under starvation conditions. Furthermore, electron micrography and JC-1 analysis revealed that IKKε konckdown resulted in aggravated mitochondrial damage and more mitochondrial ROS (mtROS) released in vitro. Notably, Western blot analysis showed that IKKε deficiency activated the TBK1 and IRF3 signaling pathways to promote pyroptosis in vitro. Collectively, our results indicate that IKKε protects against cardiomyocyte injury by reducing mitochondrial damage and NLRP3 expression following nutrition deprivation via regulation of the TBK1/IRF3 signaling pathway. This study further revealed the mechanism of IKKε in inflammation and myocardial nutrition deprivation.

Black carp IKKε collaborates with IRF3 in the antiviral signaling

Interferon regulatory factor 3 (IRF3) is activated by IκB kinase ε (IKKε) and Tank-binding kinase 1 (TBK1), which plays a crucial role in the interferon signaling in vertebrates. However, the regulation of teleost IRF3 by IKKε remains largely unknown. In this study, the IRF3 homologue (bcIRF3) of black carp (Mylopharyngodon piceus) has been cloned and characterized. The transcription of bcIRF3 was detected to increase in host cells in response to different stimuli. bcIRF3 distributed predominantly in the cytosolic area; however, translocated into nuclei after virus infection. bcIRF3 showed IFN-inducing ability in reporter assay and EPC cells expressing bcIRF3 showed enhanced antiviral ability against both grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV). Moreover, knockdown of bcIRF3 reduced the antiviral ability of the host cells, and the transcription of antiviral-related cytokines was obviously lower in bcIRF3-deficient host cells than that of control cells. The data of reporter assay and plaque assay demonstrated that bcIKKε obviously enhanced bcIRF3-mediated IFN production and antiviral activity. Immunofluorescent staining and co-immunoprecipitation assay revealed that bcIKKε interacted with bcIRF3. It was interesting that the nuclear translocation of bcIRF3 and bcIKKε was enhanced by each other when these two molecules were co-expressed in the cells, however, the protein levels of bcIRF3 and bcIKKε were decreased mutually. Thus, our data support the conclusion that bcIKKε interacts with bcIRF3 and enhances bcIRF3-mediated antiviral signaling during host innate immune activation.

TBK1 and IKKε act like an OFF switch to limit NLRP3 inflammasome pathway activation

NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation is beneficial during infection and vaccination but, when uncontrolled, is detrimental and contributes to inflammation-driven pathologies. Hence, discovering endogenous mechanisms that regulate NLRP3 activation is important for disease interventions. Activation of NLRP3 is regulated at the transcriptional level and by posttranslational modifications. Here, we describe a posttranslational phospho-switch that licenses NLRP3 activation in macrophages. The ON switch is controlled by the protein phosphatase 2A (PP2A) downstream of a variety of NLRP3 activators in vitro and in lipopolysaccharide-induced peritonitis in vivo. The OFF switch is regulated by two closely related kinases, TANK-binding kinase 1 (TBK1) and I-kappa-B kinase epsilon (IKKε). Pharmacological inhibition of TBK1 and IKKε, as well as simultaneous deletion of TBK1 and IKKε, but not of either kinase alone, increases NLRP3 activation. In addition, TBK1/IKKε inhibitors counteract the effects of PP2A inhibition on inflammasome activity. We find that, mechanistically, TBK1 interacts with NLRP3 and controls the pathway activity at a site distinct from NLRP3-serine 3, previously reported to be under PP2A control. Mutagenesis of NLRP3 confirms serine 3 as an important phospho-switch site but, surprisingly, reveals that this is not the sole site regulated by either TBK1/IKKε or PP2A, because all retain the control over the NLRP3 pathway even when serine 3 is mutated. Altogether, a model emerges whereby TLR-activated TBK1 and IKKε act like a "parking brake" for NLRP3 activation at the time of priming, while PP2A helps remove this parking brake in the presence of NLRP3 activating signals, such as bacterial pore-forming toxins or endogenous danger signals.

Peroxiredoxin 1 Interacts with TBK1/IKKε and Negatively Regulates Pseudorabies Virus Propagation by Promoting Innate Immunity

Peroxiredoxin 1 (PRDX1) is a cellular antioxidant enzyme that is crucial for diverse fundamental biological processes, such as autophagy, inflammation, and carcinogenesis. However, molecular mechanisms underpinning its diverse roles are not well understood. Here, we report that PRDX1 positively regulates interferon (IFN) induction and that pseudorabies virus (PRV) targets PRDX1 to evade IFN induction. PRV UL13 encodes a serine/threonine kinase important for PRV infection, although its biological function remains obscure. We identified PRDX1 as a UL13-interacting protein. Virological and biochemical assays demonstrate that PRDX1 promotes IFN induction by interacting with TANK-binding kinase 1 (TBK1) and IκB kinase ε (IKKε). Conversely, UL13 accelerates PRDX1 degradation via the ubiquitin-proteosome pathway in a kinase-dependent manner. In doing so, PRV inhibits IFN induction during productive infection, which requires PRDX1 expression. This study uncovers an essential role of PRDX1 in the innate immune response and reveals a new viral immune evasion strategy to counteract cellular defenses. IMPORTANCE PRV interacts with numerous cellular proteins during productive infection. Here, we demonstrated the interaction of viral protein UL13 with the antioxidant enzyme PRDX1, which functions in multiple signal transduction pathways. We found that PRDX1 participates in the type I IFN pathway by interacting with TBK1 and IKKε, thereby negatively regulating PRV propagation. However, UL13 ubiquitinates PRDX1, which routes PRDX1 into proteasomes for degradation and effectively reduces its expression. These results illuminate the fundamental role that PRDX1 plays in the IFN pathway, and they identify a potential target for the control of PRV infection.

TRAF6 Phosphorylation Prevents Its Autophagic Degradation and Re-Shapes LPS-Triggered Signaling Networks

Simple Summary

Here, we reveal that basal turnover and autophagy-induced decay of the ubiquitin E3 ligase TRAF6 is antagonized by IKKε-mediated phosphorylation at five serines. Phosphoproteomic experiments show that TRAF6 and its phosphorylation contribute to the remodeling of LPS- and autophagyinduced signaling networks, revealing an intricate link between inflammatory and metabolic processes that are frequently dysregulated in cancer.

Abstract

The ubiquitin E3 ligase TNF Receptor Associated Factor 6 (TRAF6) participates in a large number of different biological processes including innate immunity, differentiation and cell survival, raising the need to specify and shape the signaling output. Here, we identify a lipopolysaccharide (LPS)-dependent increase in TRAF6 association with the kinase IKKε (inhibitor of NF-κB kinase subunit ε) and IKKε-mediated TRAF6 phosphorylation at five residues. The reconstitution of TRAF6-deficient cells, with TRAF6 mutants representing phosphorylation-defective or phospho-mimetic TRAF6 variants, showed that the phospho-mimetic TRAF6 variant was largely protected from basal ubiquitin/proteasome-mediated degradation, and also from autophagy-mediated decay in autolysosomes induced by metabolic perturbation. In addition, phosphorylation of TRAF6 and its E3 ligase function differentially shape basal and LPS-triggered signaling networks, as revealed by phosphoproteome analysis. Changes in LPS-triggered phosphorylation networks of cells that had experienced autophagy are partially dependent on TRAF6 and its phosphorylation status, suggesting an involvement of this E3 ligase in the interplay between metabolic and inflammatory circuits.

Transient blockade of TBK1/IKKε allows efficient transduction of primary human natural killer cells with vesicular stomatitis virus G-pseudotyped lentiviral vectors

BACKGROUND AIMS

Vesicular stomatitis virus G (VSV-G)-pseudotyped lentiviral vectors (LVs) are widely used to reliably generate genetically modified, clinical-grade T-cell products. However, the results of genetically modifying natural killer (NK) cells with VSV-G LVs have been variable. The authors explored whether inhibition of the IKK-related protein kinases TBK1 and IKKε, key signaling molecules of the endosomal TLR4 pathway, which is activated by VSV-G, would enable the reliable transduction of NK cells by VSV-G LVs.

METHODS

The authors activated NK cells from peripheral blood mononuclear cells using standard procedures and transduced them with VSV-G LVs encoding a marker gene (yellow fluorescent protein [YFP]) or functional genes (chimeric antigen receptors [CARs], co-stimulatory molecules) in the presence of three TBK1/IKKε inhibitors (MRT67307, BX-795, amlexanox). NK cell transduction was evaluated by flow cytometry and/or western blot and the functionality of expressed CARs was evaluated in vitro.

RESULTS

Blocking TBK1/IKKε during transduction of NK cells enabled their efficient transduction by VSV-G LVs as judged by YFPexpression of 40-50%, with half maximal effective concentrations of 1.1 µM (MRT67307), 5 µM (BX-795) and 24.8 µM (amlexanox). Focusing on MRT67307, the authors successfully generated NK cells expressing CD19-CARs or HER2-CARs with an inducible co-stimulatory molecule. CAR NK cells exhibited increased cytolytic activity and ability to produce cytokines in comparison to untreated controls, confirming CAR functionality.

CONCLUSIONS

The authors demonstrate that inhibition of TBK1/IKKε enables the reliable generation of genetically modified NK cells using VSV-G LVs. The authors' protocol can be readily adapted to generate clinical-grade NK cells and thus has the potential to facilitate the clinical evaluation of genetically modified NK cell-based therapeutics in the future.

Expanding the View of IKK: New Substrates and New Biology

The inhibitor of kappa B kinase (IKK) family consists of IKKα, IKKβ, and the IKK-related kinases TBK1 and IKKε. These kinases are considered master regulators of inflammation and innate immunity via their control of the transcription factors NF-κB, IRF3, and IRF7. Novel phosphorylated substrates have been attributed to these kinases, a subset of which is not directly related to either inflammation or innate immunity. These findings have greatly expanded the perspectives on the biological activities of these kinases. In this review we highlight some of the novel substrates for this kinase family and discuss the biological implications of these phosphorylation events.

The VP3 Protein of Bluetongue Virus Associates with the MAVS Complex and Interferes with the RIG-I-Signaling Pathway

Bluetongue virus (BTV), an arbovirus transmitted by Culicoides biting midges, is a major concern of wild and domestic ruminants. While BTV induces type I interferon (alpha/beta interferon [IFN-α/β]) production in infected cells, several reports have described evasion strategies elaborated by this virus to dampen this intrinsic, innate response. In the present study, we suggest that BTV VP3 is a new viral antagonist of the IFN-β synthesis. Indeed, using split luciferase and coprecipitation assays, we report an interaction between VP3 and both the mitochondrial adapter protein MAVS and the IRF3-kinase IKKε. Overall, this study describes a putative role for the BTV structural protein VP3 in the control of the antiviral response.

miR-133a-3p attenuates cardiomyocyte hypertrophy through inhibiting pyroptosis activation by targeting IKKε

OBJECTIVE

Cardiac hypertrophy is an adaptive response to physiological and pathological stimuli, the latter of which frequently progresses to valvulopathy, heart failure and sudden death. Recent reports revealed that pyroptosis is involved in regulating multiple cardiovascular diseases progression, including cardiac hypertrophy. However, the underlying mechanisms remain poorly understood. This study aims to extensively investigate the regulation of miR-133a-3p on pyroptosis in angiotensin II (Ang II)-induced cardiac hypertrophyin vitro.

METHODS

The in vitro model of cardiac hypertrophy was induced by Ang II, which was validated by qPCR combined with measurement of cell surface area by immunofluorescence assay. CCK-8 assay and Hochest33342/PI staining was performed to assess pyroptosis. Dual luciferase reporter system was used to verify the direct interaction between miR-133a-3p and IKKε. The effects of miR-133a-3p/IKKε on pyroptosis activation and cardiac hypertrophy markers (Caspase-1, NLRP3, IL-1β, IL-18, GSDMD, ASC, ANP, BNP and β-MHC) were evaluated by western blot, ELISA and qPCR.

RESULTS

Ang II treatment could induce cardiomyocyte hypertrophy and pyroptosis. The expression of miR-133a-3p was repressed in Ang II-treated HCM cells, and its overexpression could attenuate both pyroptosis and cardiac hypertrophyin vitro. Additionally, IKKε expression was significantly up-regulated in Ang II-induced HCM cells. Dual luciferase reporter system and qPCR validated that miR-133a-3p directly targeted the 3'-UTR of IKKε and suppressed its expression. Moreover, IKKε overexpression impaired the protective function of miR-133a-3p in cardiomyocyte hypertrophy.

CONCLUSION

Collectively, miR-133a-3p attenuates Ang II induced cardiomyocyte hypertrophy via inhibition of pyroptosis by targeting IKKε. Therefore, miR-133a-3p up-regulation may be a promising strategy for cardiac hypertrophy treatment.

Akt phosphorylation regulated by IKKε in response to low shear stress leads to endothelial inflammation via activating IRF3

Low shear stress (LSS) plays a critical role in the development of atherosclerotic plaques and vascular inflammation. Previous studies have reported Akt phosphorylation induced by LSS. However, the mechanism and role of Akt activation remains unclear in LSS-induced endothelial dysfunction. In this study, our results demonstrated the increased phosphorylation of IKKε, TBK1 and Akt in HUVECs exposed to LSS. Furthermore, IKKε silencing using small interfering RNAs significantly reduced LSS-induced Akt phosphorylation. In contrast, silencing of TBK1 or inhibition of PI3K and mTORC2 had no effect on LSS-induced Akt phosphorylation. Notably, Akt inhibition markedly diminished LSS-induced expression of ICAM-1, VCAM-1 and MCP-1, as well as LSS-induced IRF3 phosphorylation and nuclear translocation, without affecting the activation of NF-κB and STAT1. Moreover, endothelial cell specific Akt overexpression mediated by adeno-associated virus markedly increased intimal ICAM-1 and IRF3 expression at LSS area of partially ligated carotid artery in mice. In brief, our findings suggest that LSS-induced Akt phosphorylation is positively regulated by IKKε and promotes IRF3 activation, leading to endothelial inflammation.

Molecular and spatial mechanisms governing STING signalling

Detection of microbial nucleic acids via innate immune receptors is critical for establishing host defence against pathogens. The DNA-sensing cGAS-STING pathway has gained increasing attention in the last decade as a key pathway for combating viral and bacterial infections. cGAS-STING activation primarily promotes the secretion of antiviral type I IFNs via the key transcription factor, IRF3. In addition, cGAS-STING signalling also elicits proinflammatory cytokines through NF-κB activity. Activation of IRF3 and NF-κB is mediated by the chief signalling receptor protein STING. Interestingly, STING undergoes significant trafficking events across multiple subcellular locations, which regulates both the activation of downstream signalling pathways, as well as appropriate termination of the responses. Studies to date have provided a comprehensive view of the regulation and role of the IRF3-IFN pathway downstream of STING. However, many aspects of STING signalling remain relatively poorly defined. This review will explore the current understanding of the mechanisms through which STING elicits inflammatory and antimicrobial responses, focusing on the precise signalling and intracellular trafficking events that occur. We will also discuss exciting and emerging concepts in the field, including the importance of IFN-independent STING responses for host defence and during STING-related disease.

The breast cancer oncogene IKKε coordinates mitochondrial function and serine metabolism

IκB kinase ε (IKKε) is a key molecule at the crossroads of inflammation and cancer. Known to regulate cytokine secretion via NFκB and IRF3, the kinase is also a breast cancer oncogene, overexpressed in a variety of tumours. However, to what extent IKKε remodels cellular metabolism is currently unknown. Here, we used metabolic tracer analysis to show that IKKε orchestrates a complex metabolic reprogramming that affects mitochondrial metabolism and consequently serine biosynthesis independently of its canonical signalling role. We found that IKKε upregulates the serine biosynthesis pathway (SBP) indirectly, by limiting glucose‐derived pyruvate utilisation in the TCA cycle, inhibiting oxidative phosphorylation. Inhibition of mitochondrial function induces activating transcription factor 4 (ATF4), which in turn drives upregulation of the expression of SBP genes. Importantly, pharmacological reversal of the IKKε‐induced metabolic phenotype reduces proliferation of breast cancer cells. Finally, we show that in a highly proliferative set of ER negative, basal breast tumours, IKKε and PSAT1 are both overexpressed, corroborating the link between IKKε and the SBP in the clinical context.

Long-term subcutaneous injection of lipopolysaccharides and high-fat diet induced non-alcoholic fatty liver disease through IKKε/ NF-κB signaling

Non-alcoholic fatty liver disease (NAFLD) was associated with increased level of lipopolysaccharides (LPS) which mechanism remained unclear on intervention between LPS and NAFLD. The aim was to explore the IKKε/NF-κB role and its intervention of LPS and high-fat diet (HFD) induced NAFLD. Male C57BL/6 mice were fed on high-fat diet (HFD) combined with or without simultaneously subcutaneous injection of LPS for 18 weeks. Body weight , blood biochemistry parameters, inflammatory mediator and liver lipid deposition were measured to evaluate LPS effect on NAFLD. Furthermore, IKKε selective inhibitor amlexanox (AM) was administrated by gavage to HFD + LPS induced mice. The indicators about metabolism and inflammation were examined and qRT-PCR, immunoblotting assay as well as immunohistochemistry were performed to assess IKKε/NF-κB activation and downstream gene expression. This study found that low-dose LPS + HFD aggravated more significant steatosis than simple HFD or high-dose LPS + HFD. Low-dose LPS exacerbated more prominent inflammation profile including increased IKKε and NF-κB expression in liver than HFD. Inhibiting IKKε/NF-κB signaling with amlexanox significantly prevented HFD + LPS induced metabolic disorders and hepatic steatosis. LPS-upregulated gene expression involved in glucolipid metabolism could be downregulated by amlexanox. Thus, the present study confirmed long-term combinational administration of subcutaneous low-dose LPS injection and HFD induced NAFLD model which had more significant phenotype in mice than simple HFD or high-dose LPS-induction. Targeting on IKKε/NF-κB signaling with its inhibitor amlexanox alleviated steatohepatitis, suggesting that IKKε/NF-κB signaling was responsible for effect of LPS and HFD on NAFLD.

IKKε and TBK1 in diffuse large B-cell lymphoma: A possible mechanism of action of an IKKε/TBK1 inhibitor to repress NF-κB and IL-10 signalling

The IKK‐related kinases, IKKε and TBK1, have essential roles in innate immunity in part through modifying MYD88 signalling from the Toll‐like receptors to regulate NF‐κB signalling. We investigated the expression and function of IKKε and TBK1, in diffuse large B‐cell lymphoma (DLBCL). DLBCL cell lines and patient‐derived xenografts were used to determine their sensitivity to IKKε and TBK1 inhibitors. To understand the function of IKKε and TBK1 secreted factors were determined following administration of inhibitors. Gene expression microarrays were used to determine the transcriptional effects of inhibitors. Higher TBK1 mRNA levels associated with poorer clinical outcome but IKKε and TBK1 were expressed in both germinal centre and non‐germinal centre types of DLBCL. Survival of cell lines Ly10, Ly03 and Pfeiffer, and of some primary human lymphoma cells, was suppressed by a small molecule IKKε/TBK1 inhibitor, DMX3433. DMX3433 reduced IL‐10 production from Ly10 and repressed NF‐κB mediated transcription. Inhibition of IKKε and TBK1 warrants further investigation as a potential therapeutic route to suppress NF‐κB signalling in lymphoma.

Systematic analysis of the IL-17 receptor signalosome reveals a robust regulatory feedback loop

IL‐17 mediates immune protection from fungi and bacteria, as well as it promotes autoimmune pathologies. However, the regulation of the signal transduction from the IL‐17 receptor (IL‐17R) remained elusive. We developed a novel mass spectrometry‐based approach to identify components of the IL‐17R complex followed by analysis of their roles using reverse genetics. Besides the identification of linear ubiquitin chain assembly complex (LUBAC) as an important signal transducing component of IL‐17R, we established that IL‐17 signaling is regulated by a robust negative feedback loop mediated by TBK1 and IKKε. These kinases terminate IL‐17 signaling by phosphorylating the adaptor ACT1 leading to the release of the essential ubiquitin ligase TRAF6 from the complex. NEMO recruits both kinases to the IL‐17R complex, documenting that NEMO has an unprecedented negative function in IL‐17 signaling, distinct from its role in NF‐κB activation. Our study provides a comprehensive view of the molecular events of the IL‐17 signal transduction and its regulation.

The Specific IKKε/TBK1 Inhibitor Amlexanox Suppresses Human Melanoma by the Inhibition of Autophagy, NF-κB and MAP Kinase Pathways

Inhibitor-kappaB kinase epsilon (IKKε) and TANK-binding kinase 1 (TBK1) are non-canonical IκB kinases, both described as contributors to tumor growth and metastasis in different cancer types. Several hints indicate that they are also involved in the pathogenesis of melanoma; however, the impact of their inhibition as a potential therapeutic measure in this "difficult-to-treat" cancer type has not been investigated so far. We assessed IKKε and TBK1 expression in human malignant melanoma cells, primary tumors and the metastasis of melanoma patients. Both kinases were expressed in the primary tumor and in metastasis and showed a significant overexpression in tumor cells in comparison to melanocytes. The pharmacological inhibition of IKKε/TBK1 by the approved drug amlexanox reduced cell proliferation, migration and invasion. Amlexanox did not affect the cell cycle progression nor apoptosis induction but significantly suppressed autophagy in melanoma cells. The analysis of potential functional downstream targets revealed that NF-кB and ERK pathways might be involved in kinase-mediated effects. In an in vivo xenograft model in nude mice, amlexanox treatment significantly reduced tumor growth. In conclusion, amlexanox was able to suppress tumor progression potentially by the inhibition of autophagy as well as NF-кB and MAP kinase pathways and might therefore constitute a promising candidate for melanoma therapy.

Host HDAC4 regulates the antiviral response by inhibiting the phosphorylation of IRF3

Class II HDACs, such as HDAC4, are critical regulators of the immune response in various immune cells; however, its role in innate immunity remains largely unknown. Here, we report that the overexpression of HDAC4 suppresses the production of type I interferons triggered by pattern-recognition receptors (PRRs). HDAC4 repressed the translocation of transcription factor IRF3 to the nucleus, thereby decreasing IRF3-mediated IFN-β expression. In particular, we also determined that HDAC4 can be phosphorylated and simultaneously block the phosphorylation of IRF3 at Ser386 and Ser396 by TBK1 and IKKε, respectively, by interacting with the kinase domain of TBK1 and IKKε. Furthermore, IFN-β may stimulate the expression of HDAC4. Our findings suggest that HDAC4 acts as a regulator of PRR signaling and is a novel mechanism of negative feedback regulation for preventing an over-reactive innate immune response.

TBK1 and IKKε Act Redundantly to Mediate STING-Induced NF-κB Responses in Myeloid Cells

Stimulator of Interferon Genes (STING) is a critical component of host innate immune defense but can contribute to chronic autoimmune or autoinflammatory disease. Once activated, the cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) (cGAMP) synthase (cGAS)-STING pathway induces both type I interferon (IFN) expression and nuclear factor-κB (NF-κB)-mediated cytokine production. Currently, these two signaling arms are thought to be mediated by a single upstream kinase, TANK-binding kinase 1 (TBK1). Here, using genetic and pharmacological approaches, we show that TBK1 alone is dispensable for STING-induced NF-κB responses in human and mouse immune cells, as well as in vivo. We further demonstrate that TBK1 acts redundantly with IκB kinase ε (IKKε) to drive NF-κB upon STING activation. Interestingly, we show that activation of IFN regulatory factor 3 (IRF3) is highly dependent on TBK1 kinase activity, whereas NF-κB is significantly less sensitive to TBK1/IKKε kinase inhibition. Our work redefines signaling events downstream of cGAS-STING. Our findings further suggest that cGAS-STING will need to be targeted directly to effectively ameliorate the inflammation underpinning disorders associated with STING hyperactivity.

Regulation of 8-Hydroxydaidzein in IRF3-Mediated Gene Expression in LPS-Stimulated Murine Macrophages

Cytokines and chemokines are transcriptionally regulated by inflammatory transcription factors such as nuclear factor-κB (NF-κB), activator protein-1 (AP-1), and interferon regulatory factor (IRF)-3. A daidzein derivative compound, 8-hydroxydaidzein (8-HD), isolated from soy products, has recently gained attention due to various pharmacological benefits, including anti-inflammatory activities. However, regulation of the inflammatory signaling mechanism for 8-HD is still poorly understood, particularly with respect to the IRF-3 signaling pathway. In this study, we explored the molecular mechanism of 8-HD in regulating inflammatory processes, with a focus on the IRF-3 signaling pathway using a lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid [Poly (I:C)] stimulated murine macrophage cell line (RAW264.7). The 8-HD downregulated the mRNA expression level of IRF-3-dependent genes by inhibiting phosphorylation of the IRF-3 transcription factor. The inhibitory mechanism of 8-HD in the IRF-3 signaling pathway was shown to inhibit the kinase activity of IKKε to phosphorylate IRF-3. This compound can also interfere with the TRIF-mediated complex formation composed of TRAF3, TANK, and IKKε leading to downregulation of AKT phosphorylation and reduction of IRF-3 activation, resulted in inhibition of IRF-3-dependent expression of genes including IFN-β, C-X-C motif chemokine 10 (CXCL10), and interferon-induced protein with tetratricopeptide repeats 1 (IFIT1). Therefore, these results strongly suggest that 8-HD can act as a promising compound with the regulatory function of IRF-3-mediated inflammatory responses.

IKKε phosphorylates kindlin-2 to induce invadopodia formation and promote colorectal cancer metastasis

Invadopodia formation is a key driver of cancer metastasis. The noncanonical IkB-related kinase IKKε has been implicated in cancer metastasis, but its roles in invadopodia formation and colorectal cancer (CRC) metastasis are unclear. Methods: Immunofluorescence, gelatin-degradation assay, wound healing assay and transwell invasion assay were used to determine the influence of IKKε over-expression, knockdown and pharmacological inhibition on invadopodia formation and the migratory and invasive capacity of CRC cells in vitro. Effects of IKKε knockdown or pharmacological inhibition on CRC metastasis were examined in mice. Immunohistochemistry staining was used to detect expression levels of IKKε in CRC patient tissues, and its association with prognosis in CRC patients was also analyzed. Immunoprecipitation, western blotting and in vitro kinase assay were constructed to investigate the molecular mechanisms. Results: IKKε co-localizes with F-actin and the invadopodia marker Tks5 at the gelatin-degrading sites of CRC cells. Genetic over-expression/knockdown or pharmacological inhibition of IKKε altered invadopodia formation and the migratory and invasive capacity of CRC cells in vitro. In vivo, knockdown or pharmacological inhibition of IKKε significantly suppressed metastasis of CRC cells in mice. IKKε knockdown also inhibited invadopodia formation in vivo. Clinical investigation of tumor specimens from 191 patients with CRC revealed that high IKKε expression correlates with metastasis and poor prognosis of CRC. Mechanistically, IKKε directly binds to and phosphorylates kindlin-2 at serine 159; this effect mediates the IKKε-induced invadopodia formation and promotion of CRC metastasis. Conclusions: We identify IKKε as a novel regulator of invadopodia formation and a unique mechanism by which IKKε promotes the metastasis of CRC. Our study suggests that IKKε is a potential target to suppress CRC metastasis.

IKKε-like plays an important role in the innate immune signaling of the Pacific oyster (Crassostrea gigas)

IκB-related kinase ε (IKKε) plays a crucial role in the activation of nuclear factor κB (NF-κB) by phosphorylating inhibitor of NF-κB (IκB) and in the regulation of interferon (IFN) gene expression by phosphorylating IFN regulatory factors (IRFs). In this study, we cloned an IKKε homologue cDNA (designated as CgIKKε-like) from the Pacific oyster, Crassostrea gigas. The full 2896-bp cDNA sequence comprised a 2163-bp open reading frame (ORF) encoding 720 amino acids. CgIKKε-like is ubiquitously expressed, and its mRNA levels in hemocytes after poly I:C, V. alginolyticus, or OsHV-1 μVar challenge were analyzed by real-time PCR. Compared to that in the control, CgIKKε-like mRNA expression levels were significantly increased at 3 h and peaked at 6 h after OsHV-1 μVar challenge; no obvious changes were observed in expression levels until 24 h after either V. alginolyticus or poly I:C challenge, reaching a maximum at 24 h (p < 0.01) and then rapidly decreasing. CgIKKε-like transfection into human cell lines induced NF-κB and ISRE activation, while transfection with CgIKKε-like deletion mutants abolished NF-κB and ISRE reporter gene activation. Additionally, CgIKKε-like could interact with CgTBK1 and could form homodimers strongly, which may be critical for the immune signaling transduction. Last but not least, we found that CgIKKε-like may increase CgIκBs phosphorylation and could interact with CgIRF8. Together, these results suggest that CgIKKε-like could respond to pathogenic infection, participate in the immune signal transduction and activate NF-κB and ISRE reporter genes. Thus, CgIKKε-like could play an important role in the oyster immune system.

Essential Roles for the Non-Canonical IκB Kinases in Linking Inflammation to Cancer, Obesity, and Diabetes

Non-canonical IκB kinases (IKKs) TBK1 and IKKε have essential roles as regulators of innate immunity and cancer. Recent work has also implicated these kinases in distinctively controlling glucose homeostasis and repressing adaptive thermogenic and mitochondrial biogenic response upon obesity-induced inflammation. Additionally, TBK1 and IKKε regulate pancreatic β-cell regeneration. In this review, we summarize current data on the functions and molecular mechanisms of TBK1 and IKKε in orchestrating inflammation to cancer, obesity, and diabetes.

Pharmacological inhibition of the IKKε/TBK-1 axis potentiates the anti-tumour and anti-metastatic effects of Docetaxel in mouse models of breast cancer

IκB kinase subunit epsilon (IKKε), a key component of NFκB and interferon signalling, has been identified as a breast cancer oncogene. Here we report that the IKKε/TBK1 axis plays a role in the initiation and progression of breast cancer osteolytic metastasis. Cancer-specific knockdown of IKKε in the human MDA-MB-231-BT cells and treatment with the verified IKKε/TBK1 inhibitor Amlexanox reduced skeletal tumour growth and osteolysis in mice. In addition, combined administration of Amlexanox with Docetaxel reduced mammary tumour growth of syngeneic 4T1 cells, inhibited metastases and improved survival in mice after removal of the primary tumour. Functional and mechanistic studies in breast cancer cells, osteoclasts and osteoblasts revealed that IKKε inhibition reduces the ability of breast cancer cells to grow, move and enhance osteoclastogenesis by engaging both IRF and NFκB signalling pathways. Thus, therapeutic targeting of the IKKε/TBK1 axis may be of value in the treatment of advanced triple negative breast cancer.

IKKε regulates the breast cancer stem cell phenotype

The Inhibitor of Nuclear Factor Kappa B Kinase Subunit Epsilon (IKKε) is an oncogenic protein that is up-regulated in various types of human cancers, including breast tumors. This kinase regulates diverse processes associated with malignant progression including proliferation, invasion, and metastasis. To delve into the molecular mechanisms regulated by this kinase we performed RNA-seq and network analysis of breast cancer cells overexpressing IKKε. We found that the TNF/NF-κB cascade was clearly enriched, and in accordance, NF-κB pathway inhibition in these cells resulted in a decreased expression of IKKε target genes. Interestingly, we also found an enrichment of a mammary stemness functional pathway. Upregulation of IKKε led to an increase of a stem CD44+/CD24^-/low population accompanied by a high expression of stem markers such as ALDH1A3, NANOG, and KLF4 and with an increased clonogenic ability and mammosphere formation capacity. These results were corroborated with in vivo dilution assays in zebrafish embryos which showed a significant increase in the number of Cancer Stem Cells (CSCs). Finally, we found that Triple-Negative breast tumors, which are enriched in CSCs, display higher levels of IKKε than other breast tumors, supporting the association of this kinase with the stem phenotype. In conclusion, our results highlight the role of IKKε kinase in the regulation of the stem cell phenotype in breast cancer cells, as assessed by expression, functional and in vivo assays. These results add to the potential use of this kinase as a therapeutic target in this neoplasia.

Roles for the IKK-Related Kinases TBK1 and IKKε in Cancer

While primarily studied for their roles in innate immune response, the IκB kinase (IKK)-related kinases TANK-binding kinase 1 (TBK1) and IKKε also promote the oncogenic phenotype in a variety of cancers. Additionally, several substrates of these kinases control proliferation, autophagy, cell survival, and cancer immune responses. Here we review the involvement of TBK1 and IKKε in controlling different cancers and in regulating responses to cancer immunotherapy.

vFLIP upregulates IKKε, leading to spindle morphology formation through RelA activation

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) vFLIP, a latent gene of KSHV, was first identified as a FLICE-inhibitory protein (FLIP) protecting cells from apoptosis. The vFLIP protein has been shown to activate the NF-κB signaling involved in spindle morphology formation both in HUVECs infected with KSHV and Kaposi's sarcoma (KS) itself. In this study, we independently established stably vFLIP-expressing cells and showed that they exhibited upregulated NF-κB family protein expression independent of the ability of IKKs to bind vFLIP. Further, vFLIP induced upregulation of IKKε, phosphorylation of RelA at Ser468 (p-RelA S468) and nuclear localization of Re1A concomitant with spindle morphology formation, and these effects were reversed by knockdown of IKKε and treatment with Bay-11. Overexpression of IKKε alone also showed spindle morphology formation with p-RelA S468. In conclusion, the spindle cell morphology in KS should be induced by RelA activation (p-RelA S468) by IKKε upregulation in vFLIP-expressing EA hy926 cells.

Loss of Tbk1 kinase activity protects mice from diet-induced metabolic dysfunction

OBJECTIVE

TANK Binding Kinase 1 (TBK1) has been implicated in the regulation of metabolism through studies with the drug amlexanox, an inhibitor of the IκB kinase (IKK)-related kinases. Amlexanox induced weight loss, reduced fatty liver and insulin resistance in high fat diet (HFD) fed mice and has now progressed into clinical testing for the treatment and prevention of obesity and type 2 diabetes. However, since amlexanox is a dual IKKε/TBK1 inhibitor, the specific metabolic contribution of TBK1 is not clear.

METHODS

To distinguish metabolic functions unique to TBK1, we examined the metabolic profile of global Tbk1 mutant mice challenged with an obesogenic diet and investigated potential mechanisms for the improved metabolic phenotype.

RESULTS AND CONCLUSION

We report that systemic loss of TBK1 kinase function has an overall protective effect on metabolic readouts in mice on an obesogenic diet, which is mediated by loss of an inhibitory interaction between TBK1 and the insulin receptor.

Lysine 39 of IKKε of black carp is crucial for its regulation on IRF7-mediated antiviral signaling

Interferon regulatory factor 7 (IRF7) plays a crucial role in the interferon (IFN) signaling in mammals, in which it is activated by the TBK1/IKKε complex during host antiviral innate immune response. There are few reports about the relation between IRF7 and IKKε in teleost fishes. In this study, the IRF7 homologue (bcIRF7) of black carp (Mylopharyngodon Piceus) has been cloned and characterized. The transcription of bcIRF7 gene increased in host cells in response to the stimulation of LPS, poly (I:C) and viral infection. bcIRF7 migrated around 56 KDa in immunoblot assay and was identified as a predominantly cytosolic protein by immunofluorescent staining. bcIRF7 showed IFN-inducing ability in reporter assay and EPC cells expressing bcIRF7 showed enhanced antiviral ability against both grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV). IKKε of black carp (bcIKKε) was found to be recruited into host innate immune response initiated by SVCV and GCRV in the previous work; in this paper, the kinase dead mutant of bcIKKε, bcIKKε-K39A was constructed and showed no IFN-inducing activity. The data of reporter assay and plaque assay demonstrated that bcIKKε but not bcIKKε-K39A obviously enhanced bcIRF7-mediated IFN production and antiviral activity. Our data support the conclusion that bcIKKε upregulates bcIRF7-mediated antiviral signaling, which most likely depends on its kinase activity.

Importance of Validating Antibodies and Small Compound Inhibitors Using Genetic Knockout Studies-T Cell Receptor-Induced CYLD Phosphorylation by IKKε/TBK1 as a Case Study

CYLD is a deubiquitinating enzyme that plays a crucial role in immunity and inflammation as a negative regulator of NF-κB transcription factor and JNK kinase signaling. Defects in either of these pathways contribute to the progression of numerous inflammatory and autoimmune disorders. Therefore, we set out to unravel molecular mechanisms that control CYLD activity in the context of T cell receptor (TCR) signaling. More specifically, we focused on CYLD phosphorylation at Ser418, which can be detected upon immunoblotting of cell extracts with phospho(Ser418)-CYLD specific antibodies. Jurkat T cells stimulated with either anti-CD3/anti-CD28 or PMA/Ionomycin (to mimic TCR signaling) were used as a model system. The role of specific kinases was analyzed using pharmacological as well as genetic approaches. Our initial data indicated that CYLD is directly phosphorylated by the noncanonical IκB kinases (IKKs) IKKε and TANK Binding Kinase 1 (TBK1) at Ser418 upon TCR stimulation. Treatment with MRT67307, a small compound inhibitor for IKKε and TBK1, inhibited TCR-induced CYLD phosphorylation. However, the phospho(Ser418)-CYLD immunoreactive band was still present in CRISPR/Cas9 generated IKKε/TBK1 double knockout cell lines, where it could still be prevented by MRT67307, indicating that the initially observed inhibitory effect of MRT67307 on TCR-induced CYLD phosphorylation is IKKε/TBK1-independent. Most surprisingly, the phospho(Ser418)-CYLD immunoreactive band was still detectable upon immunoblotting of cell extracts obtained from CYLD deficient cells. These data demonstrate the non-specificity of MRT67307 and phospho(Ser418)-CYLD specific antibodies, implying that previously published results based on these tools may also have led to wrong conclusions. We therefore advise to use genetic knockout studies or alternative approaches for a better validation of antibodies and small compound inhibitors. Interestingly, immunoprecipitation with the phospho(Ser418)-CYLD antibody, followed by immunoblotting with anti-CYLD, revealed that CYLD is phosphorylated by IKKε/TBK1 at Ser418 upon T cell stimulation, but that its direct detection with the phospho(Ser418)-CYLD-specific antibody in a western blot is masked by another inducible protein of the same size that is recognized by the same antibody.

IκB-Kinase-epsilon (IKKε) over-expression promotes the growth of prostate cancer through the C/EBP-β dependent activation of IL-6 gene expression

The inflammatory cytokine IL-6 has been shown to induce the nuclear translocation of androgen receptors in prostate cancer cells and to activate the androgen receptors in a ligand-independent manner, suggesting it may contribute to the development of a castrate-resistant phenotype. Elevated IL-6 serum levels have also been associated with metastasis-related morbidity in prostate cancer patients. We have previously established that over-expression of I-kappa-B-kinase-epsilon (IKKε also named IKKi or IκBKε) in hormone-sensitive prostate cancer cell lines induces IL-6 secretion. We have also reported that prostate cancer cell lines lacking androgen receptor expression exhibit high constitutive IKKε expression and IL-6 secretion. In the present study, we validated the impact of IKKε depletion on the in vitro proliferation of castrate-resistant prostate cancer cells, and characterized how IKKε depletion affects tumor growth and IL-6 tumor secretion in vivo through a mouse xenograft-based approach. We observed a significant growth delay in IKKε-silenced PC-3 cells injected in SCID mice fed with a doxycycline-supplemented diet in comparison with mice fed with a normal diet. We also found a decrease in IL-6 secretion levels that strongly correlated with tumor growth inhibition. Finally, using constructs with various IL-6-mutated promoters, we demonstrated that IKKε over-expression induces a NF-κB-independent stimulation of the IL-6 gene promoter through the activation and nuclear accumulation of the transcription factor C/EBP-β. Our study demonstrates the pro-proliferative role of the oncogene IKKε in castrate-resistant prostate cancer cell lines, involving the phosphorylation and nuclear translocation of C/EBP-β that initiates IL-6 gene expression.

IKKε and TBK1 expression in gastric cancer

Inhibitor of kappa B kinase epsilon (IKKε) and TANK-binding kinase 1 (TBK1) are non-canonical IKKs. IKKε and TBK1 share the kinase domain and are similar in their ability to activate the nuclear factor-kappa B signaling pathway. IKKε and TBK1 are overexpressed through multiple mechanisms in various human cancers. However, the expression of IKKε and TBK1 in gastric cancer and their role in prognosis have not been studied.

To investigate overexpression of the IKKε and TBK1 proteins in gastric cancer and their relationship with clinicopathologic factors, we performed immunohistochemical staining using a tissue microarray. Tissue microarray samples were obtained from 1,107 gastric cancer patients who underwent R0 gastrectomy with extensive lymph node dissection and adjuvant chemotherapy.

We identified expression of IKKε in 150 (13.6%) and TBK1 in 38 (3.4%) gastric cancers. Furthermore, co-expression of IKKε and TBK1 was identified in 1.5% of cases. Co-expression of IKKε and TBK1 was associated with differentiated intestinal histology and earlier T stage. In a multivariate binary logistic regression model, intestinal histologic type by Lauren classification and early AJCC stage were significant predictors for expression of IKKε and TBK1 proteins in gastric cancer. Changes in IKKε and TBK1 expression may be involved in the development of intestinal-type gastric cancer. The overexpression of IKKε and TBK1 should be considered in selected patients with intestinal-type gastric cancer.

In conclusion, this is the first large-scale study investigating the relationships between expression of IKKε and TBK1 and clinicopathologic features of gastric cancer. The role of IKKε and TBK1 in intestinal-type gastric cancer pathogenesis should be elucidated by further investigation.

Encephalomyocarditis virus 3C protease attenuates type I interferon production through disrupting the TANK-TBK1-IKKε-IRF3 complex

TRAF family member-associated NF-κB activator (TANK) is a scaffold protein that assembles into the interferon (IFN) regulator factor 3 (IRF3)-phosphorylating TANK-binding kinase 1 (TBK1)-(IκB) kinase ε (IKKε) complex, where it is involved in regulating phosphorylation of the IRF3 and IFN production. However, the functions of TANK in encephalomyocarditis virus (EMCV) infection-induced type I IFN production are not fully understood. Here, we demonstrated that, instead of stimulating type I IFN production, the EMCV-HB10 strain infection potently inhibited Sendai virus- and polyI:C-induced IRF3 phosphorylation and type I IFN production in HEK293T cells. Mechanistically, EMCV 3C protease (EMCV 3C) cleaved TANK and disrupted the TANK-TBK1-IKKε-IRF3 complex, which resulted in the reduction in IRF3 phosphorylation and type I IFN production. Taken together, our findings demonstrate that EMCV adopts a novel strategy to evade host innate immune responses through cleavage of TANK.

Detection of IKKε by immunohistochemistry in primary breast cancer: association with EGFR expression and absence of lymph node metastasis

Background

IKKε is an oncogenic kinase that was found amplified and overexpressed in a substantial percentage of human breast cancer cell lines and primary tumors using genomic and gene expression analyses. Molecular studies have provided the rational for a key implication of IKKε in breast cancer cells proliferation and invasiveness through the phosphorylation of several substrates.

Methods

Here, we performed immunohistochemical detection of IKKε expression on tissue microarrays constituted of 154 characterized human breast cancer tumors. We further determined the association with multiple clinicopathological parameters and 5-years overall, disease-free and distant disease free survival.

Results

We observed expression of IKKε in 60.4% of the breast cancer tumors. IKKε expression status showed no association with a panel of markers used for molecular classification of the tumors, including ER/PR/HER2 status, or with the molecular subtypes. However, IKKε expression was inversely associated with lymph node metastasis status (p = 0.0032). Additionally, we identified a novel association between IKKε and EGFR expression (p = 0.0011).

Conclusions

The unexpected observation of an inverse association between IKKε and lymph node metastasis advocates for larger scale immunohistochemical profiling of primary breast tumors to clarify the role of IKKε in metastasis. This study suggests that breast cancer tumors expressing EGFR and IKKε may be potential targets for drugs aiming at inhibiting IKKε activity or expression.

IKKε inhibits PKC to promote Fascin-dependent actin bundling

Signaling molecules have pleiotropic functions and are activated by various extracellular stimuli. Protein kinase C (PKC) is activated by diverse receptors, and its dysregulation is associated with diseases including cancer. However, how the undesired activation of PKC is prevented during development remains poorly understood. We have previously shown that a protein kinase, IKKε, is active at the growing bristle tip and regulates actin bundle organization during Drosophila bristle morphogenesis. Here, we demonstrate that IKKε regulates the actin bundle localization of a dynamic actin cross-linker, Fascin. IKKε inhibits PKC, thereby protecting Fascin from inhibitory phosphorylation. Excess PKC activation is responsible for the actin bundle defects in IKKε-deficient bristles, whereas PKC is dispensable for bristle morphogenesis in wild-type bristles, indicating that PKC is repressed by IKKε in wild-type bristle cells. These results suggest that IKKε prevents excess activation of PKC during bristle morphogenesis.

Summary: The protein kinase IKKϵ is active at the growing tip of Drosophila bristles and prevents excess PKC activation during bristle actin bundle organization and morphogenesis.

The protein kinase IKKepsilon contributes to tumour growth and tumour pain in a melanoma model

Inhibitor-kappaB kinase epsilon (IKKε) constitutes a non-canonical I-κB kinase, which amongst others modulates NF-κB activity. IKKε and NF-κB have both been described for their role in cell proliferation and their dysregulation has been associated with tumourigenesis and metastasis in multiple cancer types. Accordingly, overexpression and constitutive activation of NF-κB have also been shown in melanoma, however, the role of IKKε in this cancer type has not been investigated so far. Thus, we determined IKKε expression in malignant melanoma cells and we were able to show a significant overexpression of IKKε in tumour cells in comparison to melanocytes. Inhibition of IKKε either by shRNA or the pharmacological inhibitor amlexanox resulted in reduced cell proliferation associated with a cell cycle block in the G1-phase. Functional analysis indicated that NF-κB, Akt1 and MAPK pathways might be involved in the IKKε-mediated effects. In vivo, we applied a mouse melanoma skin cancer model to assess tumour growth and melanoma-associated pain in IKKε knockout mice as well as C57BL/6 mice after inoculation with IKKε-negative cells. In IKKε knockout mice, tumour growth was not altered as compared to IKKε wild type mice. However, melanoma associated pain was strongly suppressed accompanied by a reduced mRNA expression of a number of pain-relevant genes. In contrast, after inoculation of IKKε-depleted tumour cells, the development of melanoma was almost completely prevented. In conclusion, our data suggest that IKKε in the tumour plays an essential role in tumour initiation and progression while IKKε expression in tumour surrounding tissues contributes to melanoma-associated pain.

Molecular cloning and characterization of IKKε gene from black carp Mylopharyngodon piceus

IKKε is an IκB kinase functioning in NF-κB signal pathway in the innate immune system of higher vertebrates. To exploit the function of IKKε of black carp (bcIKKε) in its antiviral innate immunity, the IKKε gene has been cloned from the RNA isolated from the spleen of black carp. The full-length cDNA of bcIKKε is 2537 bp, which encodes the peptide of 723 amino acids. bcIKKε contains a S-Tkc domain, a PKc domain and a UBL-TBK1-like domain and bcIKKε shares the highest amino acid sequence similarity with that of grass carp. bcIKKε was constitutively transcribed in the selected tissues of black carp including gill, kidney, heart, intestine, liver, muscle, skin and spleen; and the mRNA level of bcIKKε in these tissues varied right after SVCV or GCRV infection. bcIKKε had been well expressed in HEK293T cells and western blot assay determined that this fish kinase was around 80 KDa. The immunofluorescence assay of both NH3T3 cells and EPC cells demonstrated that bcIKKε was located in the cytosolic part of the cell. Report assay result showed that overexpression of bcIKKε in EPC cells activated the expression of both zebrafish IFN and EPC IFN. All our data suggest that bcIKKε is a novel fish kinase functioning in the innate antiviral immune response of black carp.

Identification and characterization of IKKε gene from grass carp Ctenopharyngodon idella

IKKε is an IKK-related kinase implicated in antiviral immune response in higher vertebrates. To elucidate the function of IKKε in teleost fish, grass carp IKKε (gcIKKε) has been cloned and characterized in this paper. The full-length cDNA of gcIKKε is composed of 2529 nucleotides and encodes a polypeptide of 723 amino acids. The mRNA transcription of gcIKKε was constitutively detected in all the selected tissues and the gcIKKε mRNA level increased at 36 h after GCRV infection. Western blot data of both HEK293T cells and EPC cells demonstrated that gcIKKε was around 80 KDa; and immunofluorescence staining data of both NIH3T3 cells and EPC cells determined gcIKKε was a cytosolic protein. The mRNA level of gcIKKε in CIK cells was increased more than 150 times right after poly(I:C) treatment and PMA treatment triggered gcIKKε mRNA transcription in CIK cells more than 100 times. Over-expression of gcIKKε in EPC cells activated the promoter activity of both zebrafish IFN and fathead minnow IFN. gcIKKε mRNA transcription level in CIK cells was increased from 48 h post GCRV infection with different MOIs. All the data support the idea that gcIKKε is a novel teleost IκB kinase recruited in the IFN-mediated antiviral immunity of grass carp.

17β-Estradiol enhances the activation of IFN-α signaling in B cells by down-regulating the expression of let-7e-5p, miR-98-5p and miR-145a-5p that target IKKε

The activation of IFN-α signaling in B cells contributes to the pathogenesis of systemic lupus erythematosus (SLE). Many studies suggest that estrogens are closely related to the gender difference in the prevalence of SLE. However, the underlying mechanism of the interaction between estrogens and the activation of IFN-α signaling in SLE B cells remains incompletely understood. In the present study, we first found that healthy female mice showed an up-regulated type I IFN-induced gene signature in B cells compared with age-matched male mice, and an in vivo study revealed that the gender difference was related to 17β-estradiol. Moreover, we found that 17β-estradiol could enhance the activation of IFN-α signaling in an ERα-dependent manner by down-regulating the expression of three microRNAs, including let-7e-5p, miR-98-5p and miR-145a-5p. These microRNAs could target the 3'UTR of the IKKε-encoding gene IKBKE directly and regulate the expression of IKKε, which can promote the activation of IFN-α signaling. In addition, compared with age-matched male mice, female mice showed a higher level of IKKε and lower levels of let-7e-5p, miR-98-5p and miR-145a-5p in B cells. Moreover, peripheral blood mononuclear cells from women showed a higher level of IKKε and lower levels of let-7e-5p, miR-98-5p and miR-145a-5p compared with those from age-matched men. These data suggest that 17β-estradiol amplifies the activation of IFN-α signaling in B cells via IKKε by down-regulating the expression of let-7e-5p, miR-98-5p and miR-145a-5p. Our findings may provide a new perspective for understanding the mechanism underlying the gender difference in the prevalence of SLE.